With rapid increase of network traffic and bandwidth, operators have an increasingly urgent requirement for an intelligent scheduling function of a wavelength division network. Therefore, reconfigurable optical add/drop multiplexers (ROADM) are gradually used for networks of a growing quantity of high-end operators. After an ROADM is introduced onto a network, an operator can quickly provide a wavelength-level service, conveniently perform network planning, thereby reducing operation costs, and conveniently perform maintenance, thereby reducing maintenance costs.
On the other hand, on a long-haul optical transmission network, different gain or attenuation are generated on different channels (wavelengths) in a transmit band due to a plurality of reasons. Consequently, power values of wavelength signals are not equalized, thereby causing a variety of problems in network management. For example, excessively high signal power causes a larger nonlinear price, and excessively low signal power causes an excessively small optical signal-to-noise ratio (OSNR) of a signal at a receive end.
On an existing network, power equilibrium for wavelengths is usually implemented by using an optical cross device, particularly a wavelength selective switch (WSS), in each ROADM. It is assumed that, target power stipulated by a network system is 1 dB, and before wavelength signals enter an ROADM, power values of the wavelength signals are inconsistent. After wavelength signals pass through the WSS, the WSS may perform separate switching processing on the wavelength signals, and an insertion loss is additionally added to a wavelength signal whose power value is greater than 1 dB, thereby implementing optical power equilibrium for the wavelength signals. Attenuating the wavelength signal whose power value is greater than 1 dB by using phase control of a liquid crystal on silicon (LCOS) is a relatively common solution.
However, in this optical power equilibrium solution that is based on an LCOS, when a wavelength signal with high power is attenuated, power of a crosstalk signal generated in the LCOS by the wavelength signal is not reduced. Consequently, when optical power equilibrium is performed, a crosstalk feature of a port cannot satisfy a system requirement.